Laser display

ABSTRACT

A laser display system is disclosed for displaying real time data by modulating a light beam from a laser, converting the beam of light to a curved path of light and transforming the path light into successive straight lines. The straight lines of video information are then projected into a spaced relation to one another to form a display.

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Inventors Char B011) 1 App]. No. 678,!

0- 3), 7U I Patented Nov. 16, 1971 Assignee Texas instrumentsIncorporated Dallas, Tex. Original application Mar. 15, 1965, Ser. No.439,857, now Patent No. 3,549,800. Divided and this application Oct. 30,1967. Ser. No. 678,965

LASER DISPLAY 5 Claims, 6 Drawing Figs.

U.S. Cl l78/7.3. 178/7 6, 178/D1G. 2, 350/6, 350/7, 350/96. 3 50/285int. Cl l-l04n 3/08, l-i04n 9/ 14 Field of Search 178/6, DIG. 2, 7.3 D;350/96, 6, 7, 285; 178/7.6, 6, 7.85; 324/97 1295 Cited TES PATENTS .srl78/7.6 2,465,898 3/1949 Martin... 178/7.6 3.272.917 9/1966 Good.....178/54 Re.21,105, 5/1939 Round... 178/6 LCR 2,724.995 11/1955 Matnerl78/7.6 2,920.529 1/1960 Blythe 350/285 3,011,124 11/1961 Hermann...178/76 3.154.371 10/1964 Johnson 178/7.3 D 3218.390 1/1965 Bramley178/7.85 3.240.106 3/1966 Hicks 178/6 LCR 3255,35? 6/1966 Kapany 178/6LCR Primary Examiner- Robert L. Griffin Assistant Examiner-Joseph A.Orsino, Jr.

Attorneys-Samuel M. Mims, Jr., James 0. Dixon, Andrew M.

Hassell, Harold Levine, Rene E. Grossman and John-E. VandigriffABSTRACT: A laser display system'is disclosed for displaying real timedata by modulating a light beam from a laser. converting the beam oflight to a curved path of light and transforming the path light intosuccessive straight lines. The straight lines of video information arethen projected into a spaced relation to one another to form a display.

NO QRLCLASSIF PATENTEDuuv 1s IQYI 3,621 133 SHEET 1 or 2 A B G LASERLIGHT LIGHT PROJECTION SOURCE +MODULAT0RL AMER OPTICS SCREENSYNCHRONIZATION CIRCUITRY YN 5 RA N VIDEO. INPUT PATENTEDNUV 16 MI3,621,133

sum 2 BF 2 MODULATION VOLTAGE INvreN'mRS CHARLES E. BAKER BY BOB E.MARTEL LASER DISPLAY This application is a division of application Ser.No. 439,857, filed Mar. 15, 1965, now U.S. Pat. 3,549,800 in the name ofCharles E. Baker and entitled LASER DISPLAY.

This invention relates to projection display systems and moreparticularly to a display system using a laser light source.

Laser light sources offer advantages not found in conventional lightsources, the significant distinguishing properties being: highintensity, spacial coherence, monochromaticity and polarization. Some ofthese features may be more important than others depending upon theapplication. For example, the lasers high intensity together with thespacial coherence removes the necessity of using larger aperture opticsfor efficient energy transfer. At best, perhaps a few percent of thelight from a tungsten filament may be used in a conventionaltransparency projector. Essentially all the light from the laser isusable, and several scanning and light modulation techniques make use ofthe laser spectral purity or the linear polarization of its output.

It is therefore an object of the invention to provide an improveddisplay system in which a laser light source is employed.

Another object of the invention is to provide a display system in whicha laser light beam is modulated and scanned to produce an image whichmay be projected onto a viewing screen.

Another object of the invention is to provide a display system havingimproved intensity and resolution.

Another object of the invention is to provide a display which may bemore efficiently projected.

Another object of the invention is to provide a display system capableof projecting a television picture of greater size than has beenpractical heretofore.

Another object of the invention is to provide an apparatus for producinghorizontal and vertical scanning of a modulated light beam.

Another object is to provide means for transforming a modulated lightbeam into a linear horizontal trace of light.

Other objects and features of the invention will be apparent from thefollowing detailed description when read in conjunction with theappended claims and attached drawings, in which:

FIG. 1 is a functional layout of the laser display system of theinvention;

FIG. 2 is a functional block diagram of the display system;

FIG. 3 is a fiber bundle used in the optical transmission of light;

FIG. 4 is a diagram showing the light modulation and optical system;

FIG. 5 is a drawing depicting a circular resonance scanner; and

FIG. 6 is a drawing of a galvanometer light beam scanner.

The laser display system described herein is adapted for the projectionof commercially produced television pictures, which requires that thehorizontal and vertical scan rates be the same as those used inconventional television equipment. However, this identity of scan ratesis not a limiting feature of the invention. A standard TV displaynormally has 525 active vertical lines, whereas a vertical resolution inexcess of 1,000 lines and beyond is possible with the present invention.

Referring now to FIG. 1 of the drawings, the basic layout of thecomplete laser display system is shown. The laser is operated in ahemispherical geometry so that all the output is generated in a singlespacial mode. This allows a diffractionlimited optical system to beused, and assures maximum resolution with a limited optical aperture.The lens 2 is used to diverge the light emitted from the laser 1. Thelight is collimated through lens 3, projected through the modulator 4and polarizer 5 onto a rotating rnirrgr g which is part of thehorizontal scanner 7. secansfif the motion of the mirror, the modulatedlig t beam is reflected in a circular pattern onto end 8 ofthe fiberoptic device 9.

The horizontal scanner 7 generates a lissajous pattern at 15,750 cyclesper second, which is the horizontal TV line rate.

This is accomplished by driving the two axes of the scanner with 15,750-cycles-per-second sine waves which are out of phase. This circular scanpattern is then rectified by fiber optic device 9 into a linear linescan with near zero flyback time. This is possible since the light beamis projected in the circular lissajous pattern from mirror 6 onto thecircular portion 8 of fiber optic device 9. The light beam travelsthrough the fibers making up the fiber optic assembly and is projectedout the end 10 of the optic fibers onto the oscillating mirror 11. Inpassing through the fiber optic device 9, the light beam is scatteredand emerges as an 174 cone of light. Because of this scattering, thevertical scanner mirror lI-must be considerably larger and turii through a larger angle than the horizontal scanner.

A darsonval-type galvanometer is used to produce the vertical scan whichis explained hereinafter. The reflection from the mirror 11 is projectedthrough projection lens 12 onto an ordinary light screen (not shown).

FIG. 2 is a block diagram of the laser display system. A light beamgenerated within the laser A is modulated by modulator B. The modulatoris driven by a video amplifier C which amplifies the video input signalto a level suitable for acting upon the modulator. The modulated lightbeam is then transformed into horizontal segments by the scanner F andprojected by the projection optics G onto a screen H. The video inputsignal includes a synchronization pulse which is used in synchronizingthe horizontal and vertical scanners. The sync pulse is separated fromthe video signal by the sync separation circuitry D and applied to thesynchronization and driving circuitry E. Responsive to the signal fromthe synchronization and driving circuitry, the horizontal and verticalscanners operate synchronously to change the modulated light beam intomodulated line segments which are combined to form a display.

There are three basic types of lasers; solid-state gaseous andsemiconductor injection. Although all three can be operated continuouslyonly the gas laser can be operated continuously without employingcryogenic cooling techniques.

Since the laser beam is monochromatic, the use of a single laser willproduce a projection in one color. The neon-helium gas laser produces aruby-red light, as does the krypton laser. Blue and green lights may beproduced by an argon laser. Full color displays are possible bycombining the output of three lasers; a neon-helium or krypton laserproducing a red light, and twodifferent argon lasers producing blue andgreen light, the combination of the three producing white light or anycolor combination thereof.

One particular laser used in producing a display system was a 50-milliwatt helium-neon gas laser model 125 produced by Spectra-Physics,Mountain View, California The resonator mirrors and plasma tube of thelaser were mounted on a rigid structure with suitable adjustments toallow easy alignment. Radiofrequency excitation was used in addition toDC excitation in increase the power output by 25 percent. Thehemispherical resonator was operated in the uniphase or TEM mode. Othermodes were discriminated against by proper mirror orientation. All thepower was taken out of the spherical end by using a flat mirror on theopposite end with a extremely high reflectivity. The power output of thelaser was not necessarily a limiting factor; however, the larger theprojection and the greater the intensity, the greater the power thelaser would have to produce.

Light modulator B, FIG. 2 was made of two matched pieces of 45Z-cut KDPoriented at a 90 angle for temperature compensation. This modulator isdisclosed in patent application, Ser. No. 371,053, filed May 28, 1964,now U.S. Pat. No. 3,402,002 and assigned to the same assignee as thepresent application. A modulator of this type can be operated at 75percent modulation efficiency over a S-megacycle bandwidth with 600-8.peak voltage with a contrast of greater than to I. In the operation ofthe modulator, the collimated polarized light from the Ne-I-Ie laserpasses down the axis of the modulator crystal and an electric field isapplied to the modulator, producing elliptical polarization of theemerging light.

FIG. 4 shows the laser, modulator and polarizer. The linearly polarizedlight from the laser 1 passes through the modulator 4 and emerges with avariable amount of elliptical polarization due to the modulating of thelight beam. A polarizer 5, oriented perpendicular to the input polarizedlight, converts the varying elliptically polarized light into linearlypolarized amplitude-modulated light. By selecting an initial biasvoltage, almost no light is allowed to pass through the modulator. Agood polarizer may have a transmission as low as 10 in the crossed-axiscondition. A video signal applied to the modulator can then allow fromto nearly I00 percent of the incident light to pass through themodulator.

The video amplifier, block C along with the synchronization and drivingcircuitry, block E, and sync separator, block D, are all conventionalcircuitry as used in present-day television systems. The high-levelvideo amplifier C drives the light modulator 8 while the synchronizationcircuitry E is necessary to form a -stable display and provide suitabledriving waveforms for the light beam scanner F. The video amplifiershould supply 500 volts or more peak voltage to the light modulator froma l.5-volt video input. A two-stage video amplifier of conventionaldesign is used with DC restoration to provide the highest possiblequality display.

The projection optics, blocks F and G, include the horizontal scanner,the fiber optic device, and the vertical scanner. The horizontalscanner's primary function is to convert the light beam into a circulartrace. It is well known that various patterns may be generated byselecting combinations of voltages which have differing phaserelationships. One example of this is the lissajous patterns which maybe generated on the face of an oscilloscope. By combining two sinusoidalwaves of equal magnitude, 90 out of phase, a circle may be generated.Using this principle, the scanner in FIG. 5 was developed. Thehorizontal scanner consists primarily of a piezoelectric transducerdriver 21, a resonant fiber and a mirror 6. The piezoelectric transducerdrives the resonant fiber, which has a mirror 6 attached to the endthereof. The resonant fiber acts as a mechanical transformer amplifyingthe deflection of the transducer caused by applying two sinusoidalsignals 90 out of phase to the transducer. The transformed motion causesthe mirror to rotate in a circular mode.

The transducer is a standard lead titanate zirconate (PZT) piezoelectrictransducer such as Clevite No. 60099, and the resonant fiber is, forexample, a 0.0l0-inch diameter quartz rod. The mirror is a 0.050 -inchdiameter circular concave mlrror.

The horizontal scanner is not limited to a piezoelectric transducer. Amirror may be suspended upon two wires placed 90 to each other. Byplacing the suspended mirror in a magnetic field and driving both wireswith two sinusoidal currents 90 out of phase, the mirror is deflectedsubstantially in a plane in such a manner as to produce a circular scan.

The light beam impinging on the mirror 6 is therefore converted into acircular pattern which is projected upon the end 8 of the fiber opticdevice 9. The fiber optic device 9 is shown in FIG. 3. The function ofthe device is to provide a scan rectification to convert the circularlight pattern projected from the horizontal scanner into a linear sweepwith near-zero flyback time. Light impinging on one end ofa fiber withinthe fiber optic device will be radiated through the fiber and be emittedat the other end. interference between fibers by light of one fiberradiating into the other is eliminated by coating each fiber with anopaque material. The fiber optic assembly 9 consists ofa layer ofoptical fibers flat at one end and bent to form a circular array 8 atthe opposite end. The unit is constructed from multifiber ribbons. Amultifiber may consist of, for example, a 6X6 array of opticallydistinct 10- micron coated fibers fused into a single strand. Thesestrands are then cemented side by side to form a ribbon. A number ofribbons are clamped together to form the linear end, and the circularend is formed by wrapping the ribbons around a tube end securing themwith a shrink-fit plastic sleeving. After potting with epoxy ribbon, thescan converter is completed by polishing the ends. Various means offabricating the fiber optic may be utilized, but the above-mentionedmeans has been found to be the simplest. The shape is not limited to theone shown in the FIGS. of the drawings, but may be formed into anyrequired configuration.

The linear sweep projection from the end 10 of the fiber optic device 9is projected onto mirror 1! of the vertical scanner. One basicconfiguration of this scanner is shown in FIG. 1.

In the development of the vertical scanner, both piezoelectric andelectromagnetic devices were used. One approach was to reflect the beamvertically with a piezoelectric driven mirror, in which two bimorphpiezoelectric transducers were used as flexture elements for the drivingmirror 11.

The scanner used in this embodiment of the invention was a galvanometerlight beam device as shown in FIG. 6. Therein depicted is a magnet 31having pole pieces 32 and 33. Between the pole pieces is coil 34, whichis a suspended torsion wire 35, thus eliminating the need for bearings.Mounted upon the coil and extending therefrom is the mirror 11. Thismirror receives the light from the end 10 of fiber optic device 9 andprojects it through a projection lens 12 to produce the vertical scan.The mirror oscillates back and forth projecting each line of thehorizontal scan onto the screen. This method of achieving a linear tracewith rapid flyback works quite well with the present system. A flybacktime of less than 1 millisecond together with a deflection of greaterthan 10 has been possible with small mirrors. The galvanometer is drivenwith positive and negative current pulses combined with a sawtoothwaveform.

Although the present invention has been shown and illustrated in termsof specific preferred embodiments, it will be apparent that changes andmodifications are possible without departing from the spirit and scopeof the invention as defined in the appended claims.

What is claimed is:

I. In a projection system including substantially diffractionlimitedoptical means for transforming a modulated laser light beam operating inthe uniphase mode into successive horizontal traces, said optical meanshaving an aperture sized to pass substantially only the uniphase mode ofsaid light beam and comprising the combination ofa mirror driven so asto project said modulated light beam into a series of circular traces, afiber optic device for receiving said circular traces of modulated lightand transforming them into a series of horizontal line segments ofmodulated light, and an oscillating vertical scan mirror for receivingsaid horizontal line segments and projecting them in spaced relationshipwith each other to form a display.

2. A display system comprising in combination laser means operable inthe uniphase mode for emitting a visible light beam,

a substantially diffraction-limited optical system having an aperturesized to pass substantially only the uniphase mode of said light beamwhich includes means for modulating said light beam,

a horizontal scanner to convert said modulated light beam into acircular pattern,

a fiber optic device to transform said circular pattern into a linearhorizontal trace, and

a vertical scanner to project successive horizontal traces in a spacedrelationship to each other to form a display.

3. A display system comprising in combination laser means operable inthe uniphase mode for emitting a visible light beam,

means for modulating said light beam, a substantiallydiffraction-limited optical system having an aperture sized to passsubstantially only the uniphase mode of said light beam which includes ahorizontal scanner to convert said modulated light beam into a circularpattern,

a fiber optic device to transform said circular pattern into a linearhorizontal trace, and

a vertical scanner to project successive horizontal traces in a spacedrelationship to each other to form a display.

4. A display system comprising in combination laser means operable inthe uniphase mode for producing a visible light output having at leasttwo colors,

a substantially diffraction-limited optical system having an aperturesized to pass substantially only the uniphase mode of said light outputwhich includes means for modulating said light output,

a horizontal scanner to convert said modulated light output into acircular pattern,

a fiber optic device to transform said circular pattern into a linearhorizontal trace, and

a vertical scanner to project said successive horizontal traces in aspaced relationship to each other to form a color display.

5. A display system comprising in combination laser means operable inthe uniphase mode for producing a visible light output having at leasttwo colors,

means for modulating said light output in accordance with video signals,

a substantially diffraction-limited optical system having an aperturesized to pass substantially only the uniphase mode of said light outputwhich includes a horizontal scanner to convert said modulated lightoutput into a circular pattern,

a fiber optic device to transform said circular pattern ihto a linearhorizontal trace, and a vertical scanner to project said successivehorizontal traces in a spaced relationship to each other to form a colordisplay.

1. In a projection system including substantially diffractionlimitedoptical means for transforming a modulated laser light beam operating inthe uniphase mode into successive horizontal traces, said optical meanshaving an aperture sized to pass substantially only the uniphase mode ofsaid light beam and comprising the combination of a mirror driven so asto project said modulated light beam into a series of circular traces, afiber optic device for receiving said circular traces of modulated lightand transforming them into a series of horizontal line segments ofmodulated light, and an oscillating vertical scan mirror for receivingsaid horizontal line segments and projecting them in spaced relationshipwith each other to form a display.
 2. A display system comprising incombination laser means operable in the uniphase mode for emitting avisible light beam, a substantially diffraction-limited optical systemhaving an aperture sized to pass substantially only the uniphase mode ofsaid light beam which includes means for modulating said light beam, ahorizontal scanner to convert said modulated light beam into a circularpattern, a fiber optic device to transform said circular pattern into alinear horizontal trace, and a vertical scanner to project successivehorizontal traces in a spaced relationship to each other to form adisplay.
 3. A display system comprising in combination laser meansoperable in the uniphase mode for emitting a visible light beam, meansfor modulating said light beam, a substantially diffraction-limitedoptical system having an aperture sized to pass substantially only theuniphase mode of said light beam which includes a horizontal scanner toconvert said modulated light beam into a circular pattern, a fiber opticdevice to transform said circular pattern into a linear horizontaltrace, and a vertical scanner to project successive horizontal traces ina spaced relationship to each other to form a display.
 4. A displaysystem comprising in combination laser means operable in the uniphasemode for producing a visible light output having at least two colors, asubstantially diffraction-limited optical system having an aperturesized to pass substantially only the uniphase mode of said light outputwhich includes means for modulating said light output, a horizontalscanner to convert said modulated light output into a circular pattern,a fiber optic device to transform said circular pattern into a linearhorizontal trace, and a vertical scanner to project said successivehorizontal traces in a spaced relationship to each other to form a colordisplay.
 5. A display system comprising in combination laser meansoperable in the uniphase mode for producing a visible light outputhaving at least two colors, means for modulating said light output inaccordance with video signals, a substantially diffraction-limitedoptical system having an aperture sized to pass substantially only theuniphase mode of said light output which includes a horizontal scannerto convert said modulated light output into a circular pattern, a fiberoptic device to transform said circular pattern into a linear horizontaltrace, and a vertical scanner to project said successive horizontaltraces in a spaced relationship to each other to form a color display.